President Trump has told the Pentagon to take another look at missile defense. Technology to shoot down missiles has existed for decades, but the kind of missile shield Trump is looking to build would be much more complex – and expensive.

A key part of the new missile defense system, which Trump described as “Golden Dome” in a speech earlier this year, will likely be space-based interceptors, according to experts and an executive order signed by the president.

A number of defense companies have expressed interest in trying to build the Golden Dome. Last week, Reuters reported that Elon Musk’s firm SpaceX had joined a bid for the project. Musk later refuted that claim in a post on X.

Here’s why a critical part of Golden Dome might be built on the final frontier, and what building such a system would involve.